(1) Field of the Invention
This invention relates to molding apparatus for forming by molding the coil of a stator of a rotary electric machine, such as an electric motor, generator, etc., and more particularly it deals with the construction of a mold for forming the coil.
(2) Description of the Prior Art
In recent years, the concept of impregnating the coil of a stator of a rotary electric machine with a synthetic resinous material or applying a coat of such material to the coil for insulating or fixing same has become popular. In this case, there is raised the problem that what construction should the mold have or where the channels for injecting the resinous material should be located for improving productivity.
First of all, the idea came to mind was to cover the stator core and coil of the rotary electric machine completely with a resinous material. When the stator is covered with a resinous material, there is latitude to a certain extent in selecting the channels through which the resinous material is injected. However, this proposal has the disadvantages that a large volume of resinous material is consumed and the rotary electric machine becomes high in cost, and that it becomes difficult to obtain a compact overall size in a rotary electric machine.
The idea next came to mind was to limit the impregnation or coating of the stator to a position in the periphery of the coil, to reduce the consumption of the resinous material. In this case, the channels for injecting the resinous material therethrough into the machine can be advantageously provided in cutouts formed in the outer periphery of the stator core which is not in the form of a complete circle. An example of the mold based on this idea will be outlined by referring to FIGS. 1 and 2. As shown, the numeral 1 designates a stator including a stator core 2 having a coil 3 wound thereon. A mold includes a lower mold member 4 and an upper mold member 5. An intermediate mold member 6 for arranging runners 7 along cutouts formed in the stator core 2 is formed with a groove along the outer periphery of the stator core 2. The numeral 8 designates an intermediate mold member presser for forcing the intermediate mold member 6 against the outer periphery of the stator core 2. The lower mold member 4 includes a core 9 fitted to the inner periphery of the stator core 2, a groove 10 for positioning the intermediate mold member 6 around the stator core 2, and an inner surface 11 in spaced juxtaposed relation to the coil 3. Likewise, the upper mold member 5 includes an inner surface 12 in spaced juxtaposed relation to the coil 3, and a projection 13 positioned against the end surface of the core 9. A sprue 14 is formed in the upper mold member 5 and communicates with a space 15 defined by the upper mold member 5 and surrounding the coil 3, the outer peripheral surface of the stator core 2 and the intermediate mold member 6.
The process for molding the stator 1 by using the mold of the aforesaid construction will now be described. The stator core 2 is fitted at its inner peripheral surface to the core 9 of the lower mold member 4 and inserted until the inner peripheral side of the lower end surface of the stator core 2 abuts against an offset portion 16 of the core 9. Then the intermediate mold member 6 is engaged in the groove 10 and fixed around the stator core 2 by moving the intermediate mold member presser 8. Thereafter the upper mold member 5 is moved downwardly until the outer peripheral side of the end surface of the projection 13 of the upper mold member 5 abuts against the inner peripheral side of the upper end surface of the stator core 2. A resinous material in a molten state in injected under pressure through the sprue 14, to fill the space 15 with the resinous material and a space 17 formed in the lower mold member 4 through a slot and the runners 7 in the stator core 2. The stator 1 that has been molded can be removed following breakdown of the mold after the resinous material has set.
Some disadvantages are associated with the mold of the aforesaid construction. The mold is complex in construction and low in operation efficiency. It is a time-consuming operation to assemble and disassemble the stator 1 with the mold. A variation in the thickness of the stator core 2 occurring when it is fitted to the core 9 could not be accommodated, making it impossible to keep the mold airtight. For example, when the stator core 2 has an increased thickness when fitted to the core 9, gaps would be formed between the end surfaces of the core 9 and the projection 13 and between the upper die member 5 and intermediate die member 6 respectively, so that the resinous material would leak through the gaps from the mold cavity. Thus it has been essential to obtain a correct thickness of the stator core 2 when fitted to the core 9 of the lower mold member 4 because the molding operation would have to be interrupted under such condition.